Apparatus and method for selective laser-applied cladding

ABSTRACT

A method for applying a wear-resistant material to a rock bit is disclosed that includes depositing a coating on a selected area of the rock bit, applying a heated wear-resistant material using a laser assisted cladding apparatus to a selected portion of the rock bit, wherein the coating is selected to have material properties to prevent significant bonding between the heated wear-resistant material and the coated area of the rock bit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. § 119 to U.S.Provisional Application Ser. No. 60/494,876, filed on Aug. 13, 2003.This provisional application is hereby incorporated by reference in itsentirety.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates generally to methods and apparatus for depositinga material on a substrate. More specifically, the invention relates tomethods and apparatus for depositing a wear resistant layer on asubstrate.

2. Background Art

Drilling in the earth is commonly accomplished by using a drill bithaving a plurality of rock bit roller cones (“cutter cones”) that areset at angles relative to the drill string axis. The bit essentiallycrushes the formations through which it drills. The roller cones rotateon their axes and are, in turn, rotated about the main axis of the drillstring. In drilling boreholes for oil and gas wells, blast holes, andraise holes, rock bit roller cones constantly operate in a highlyabrasive environment. This abrasive condition exists during drillingoperations even with the use of a medium for cooling, circulating, andflushing the borehole. Such a cooling medium may be either drilling mud,air, or another liquid or gas.

When drilling a hard formation, a bit with tungsten carbide insertsprojecting from the body of a rolling cone generally is utilized due tothe inserts' relative hardness. However, the carbide inserts are mountedin a relatively soft metal (e.g. steel) that forms the body of therolling cone. This relatively soft body may be abraded or eroded awaywhen subjected to the high abrasive drilling environment. This abrasionor erosion occurs primarily due to the presence of relatively finecuttings and chips from the formation that are in the borehole.

Additional causes include the direct blasting effect of the drillingfluid used in the drilling process, and the rolling or sliding contactof the cone body with the formation. When the material supporting theinserts is substantially eroded or abraded away, the drilling forceseither may break the inserts or may force them out of the rolling conebody. As a result, the bit is no longer effective in cutting theformation. Moreover, the inserts that break off from the rolling conemay further damage other inserts, the rolling cones, or other parts ofthe bit, eventually leading to a catastrophic failure.

Erosion of the rolling cone body usually is most pronounced on the innerand outer edges of the lands of the cone surface. This area isimmediately adjacent to the insert and the groove between two rows ofinserts. The heaviest wear on the rolling cone surface lands is usuallyon the inner edges of the outer rows and on the outer edges of the innerrows. When drilling relatively soft but abrasive formations, the bit isable to penetrate at an extremely high rate. This can result inindividual cutting inserts penetrating entirely into the abrasiveformation, causing the formation to come into contact with the coneshell body.

When such abrasive contact occurs, the relatively soft cone shellmaterial will wear away at the edges of the surface lands until theinterior portion of the insert becomes exposed. The retention ability ofthe cone body is reduced, thereby ultimately resulting in the potentialloss of the inserts and reduction of bit life. Because the penetrationrate is related to the condition of the bit, the drill bit life andefficiency are of paramount importance in the drilling of boreholes.Accordingly, various methods of hardfacing rock bit cones for erosion orabrasion protection have been attempted.

For example, thermal spraying has been used to coat the entire exposedsurfaces, including the inserts, of a rolling cone with a hardfacingmaterial. Another method involves placing small, flat-top compacts ofhard material in the vulnerable cutter shell areas to prevent coneerosion. Since erosion of groove surface can be the main cause of insertloss, methods have been developed to apply hardfacing material to boththe lands and the grooves of a roller cone.

It should be noted that inserts are typically retained in a roller coneby the interfacial tension generated when the insert is press-fittedinto a drilled hole in the rolling cone body. Accordingly, any methodused to alleviate the erosion of the rolling cone must take intoconsideration that the interfacial tension holding the insert must beretained.

FIG. 1 illustrates a typical prior art rock bit for drilling boreholes.The rock bit 10 has a steel body 20 with threads 14 formed at an upperend and three legs 22 at a lower end. Each of the three rolling cones 16are rotatably mounted on a leg 22 at the lower end of the body 20. Aplurality of cemented tungsten carbide inserts 18 are press-fitted orinterference fitted into insert sockets formed in the cones 16.

When in use, the rock bit is threaded onto the lower end of a drillstring (not shown) and lowered into a well or borehole. The drill stringis rotated by a rig rotary table with the carbide inserts in the conesengaging the bottom and side of the borehole 25 as shown in FIG. 2. Asthe bit rotates, the cones 16 rotate on the bearing journals 19 andessentially roll around the bottom of the borehole 25. The weight on thebit is applied to the rock formation by the inserts 18 and the rock iscrushed and chipped by the inserts. A drilling fluid is pumped throughthe drill string to the bit and is ejected through nozzles 26 (shown inFIG. 1). The drilling fluid then travels up the annulus formed betweenthe exterior of the drill pipe and the borehole 25 wall, carrying withit most of the cuttings and chips. In addition, the drilling fluidserves to cool and clean the cutting end of the bit as it works in theborehole 25.

FIG. 2 shows the lower portion of the leg 22 which supports a journalbearing 19. A plurality of cone retention balls (“locking balls”) 21 androller bearings 12 a and 12 b surround the journal 19. An O-ring 28,located within an O-ring groove 23, seals the bearing assembly.

The cone includes multiple rows of inserts, and has a heel portion 17located between the gage row inserts 15 and the O-ring groove 23. Aplurality of protruding heel row inserts 30 are about equally spacedaround the heel 17. The heel row inserts 30 and the gage row inserts 15act together to cut the gage diameter of the borehole 25. The inner rowinserts 18 generally are arranged in concentric rows and they serve tocrush and chip the earthen formation.

As used herein, the term “erosion” will refer to both erosion and otherabrasive wear. Much of the erosion of the cone body typically occursbetween the gage row inserts 15 and heel row inserts 30. Furthermore,erosion also may occur at the lands 27 between the gage row inserts 15and inner row inserts 18. Generally, a “land” refers to a surface on arolling cone where insert holes are drilled on the cone. It is alsopossible that erosion may occur in the grooves 24 between successiveinner row inserts 18. These areas on a rolling cone surface arecollectively referred to as “areas susceptible to erosion.” Erosion inthese areas may result in damage to the cone and/or loss of the inserts.In highly erosive environments, the whole cone body may be subjected tosevere erosion and corrosion.

As noted above, a number of methods have been proposed for applying ahardfacing layer to the surfaces of the cones. In particular, lasercladding is a material deposition technique where the energy of a laseris used to deposit a well-bonded hardfacing layer onto a substrate. Forwear resistant applications, this layer tends to be formed of compositematerials containing one or more hard phases dispersed in a relativelysofter matrix. Many such hardfacing materials are known in the art, forexample, U.S. Pat. No. 6,196,338, assigned to the assignee of thepresent invention.

Typical prior art techniques involving laser cladding involve depositinga cladding material using a first, non-laser technique, and then laserfusing the cladding material to the substrate. U.S. Pat. No. 4,781,770discloses one typical prior art technique. That patent discloses, withreference to FIG. 3, that a plurality of insert retention holes 146 aredrilled in the exterior shell 128. Typically, the insert holes aredrilled to be approximately 0.003 inch smaller in diameter than the hardcutter inserts 142, which are to be press fitted into the holes 146.

A force of approximately several thousand pounds may be required topress the cutter inserts 142 into place in the insert holes 146. In the'770 patent, the finished cone 120 is sprayed with cladding material 154in the form of powder through a nozzle 160 (referencing FIG. 4). Thepowder may be a mixture of carbides in a matrix, which may be blendedwith an organic mixture, such as cellulose acetate, to facilitateadhesion to the cone surface 128 during spraying. Alternatively, a highvelocity plasma spray may be used to spray the powder 154, as shown inFIG. 3. The powder spray unit is not shown. The powder is then densifiedand fused with a laser source 150 (see FIG. 3). Further, the '770 patentdiscloses that the entire exterior shell 128 of the intermediate steelbody 144 is treated with the laser beam 152 in a raster pattern by usinga mechanical scanner.

However, laser cladding the entire cone surface is problematic in thatif cracks develop in the cladding, they will invariably lead to cracksin the inserts, leading to early bit failure. What is needed, therefore,are apparatus and methods for depositing a hardfacing layer on a cone,without damaging either the surface of the cone, or the inserts affixedthereto.

SUMMARY OF INVENTION

In one aspect, the present invention relates to a method for applying awear-resistant material to a rock bit that includes depositing a coatingon a selected area of the rock bit, and applying a heated wear-resistantmaterial using a laser assisted cladding apparatus to a selected portionof the rock bit, wherein the coating is selected to have materialproperties to prevent significant bonding between the heatedwear-resistant material and the coated area of the rock bit.

In one aspect, the present invention relates to a coated insert for usein cladding applications that includes a substrate, and a coatingdeposited on at least one portion of said substrate in an amountsufficient to reduce bonding of a wear resistant material to saidsubstrate, wherein the coating is a carbide, a boride, or a nitride of ametal selected from group IVA, VA, VIA transition metal.

In one aspect, the present invention relates to a method of fabricatinga drill bit that includes forming a body of the drill bit, forming aplurality of holes in portions of the body to receive coated inserts,inserting a plurality of coated inserts into said plurality of holes,and cladding at least one selected area of said body with a wearresistant material, wherein the cladding comprises using alaser-assisted cladding apparatus to deposit the wear resistant materialin a single step.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a prior art drill bit;

FIG. 2 shows a cross-section of a single leg and cone of the prior artdrill bit of FIG. 1;

FIG. 3 illustrates a prior art laser cladding technique;

FIG. 4 illustrates a prior art laser cladding technique;

FIG. 5 a illustrates a cone in accordance with one embodiment of thepresent invention;

FIG. 5 b illustrates one embodiment of a laser assisted claddingapparatus in accordance with the present invention;

FIG. 6 illustrates a coated insert in accordance with an embodiment ofthe present invention;

FIG. 7 illustrates an automated system including a computer, inaccordance with an embodiment of the present invention;

FIGS. 8 a and 8 b illustrate an apparatus for laser cladding inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The present invention relates to apparatus and methods for laser-appliedcladding. In particular, embodiments of the present invention providemethods and apparatus for applying cladding to selected cone surfacesand/or leg surfaces in rotary mining bits. As used herein, the term“cladding” refers to the wear resistant material that may be applied toa substrate, or to the act of depositing the material. “Claddingprocess” is an alternative term given to the process of depositingcladding to form a “cladding layer” on the surface of the substrate.“Coating” is used to refer to a protective coating which may be appliedto selected surfaces of the substrate, to prevent significant bondingbetween the cladding and the substrate, it is also used to refer to theprocess of applying a coating. As used herein, the term insert is notintended to be limited to an insert for a roller cone bit but isgenerally used to refer to any cutting element to be inserted into acutting tool, such as a cutter inserted into a fixed cutter bit.Further, embodiments of the present invention relate to inserts for usein rock bit applications. As used herein, the term “rock bit” expresslyincludes roller cone bits, fixed cutter bits, or any other type of bitfor cutting through earth formations.

Thus, instead of applying cladding only to the desired portions of thedrill bit, as is typical in the prior art, cladding may be applied tothe entire bit with a special coating on those sections where it is notdesired to have cladding. The coating prevents the cladding from bondingto the substrate, leaving cladding on the desired portion only.

By “selected” the inventors mean the selective placement of cladding orselectively bonding the cladding to a substrate. Selective placementmeans that the cladding is applied to selected areas, while selectivebonding involves pre-coating the substrate with a material that preventsthe cladding from bonding to selected areas. Thus, some embodiments ofthe present invention provide techniques for providing cladding with asignificant difference in bond strength of the cladding in an uncoatedregion and a coated region.

In accordance with embodiments of the invention, a coating is used thatsignificantly decreases the bond strength of the cladding to the coatedregion as compared to an uncoated region. Afterwards, cladding may bedeposited over an entire surface. The cladding will not significantlybond to the coated regions, and can easily be removed or allowed to falloff.

It should be noted that, while the description provided below references“insert bits,” it is expressly within the scope of the present inventionthat the methods and apparatus described herein may be used moregenerally to deposit cladding on a substrate. In general, techniques andapparatus disclosed by the present invention may be used wherever theselected application of a wear resistant compound to a substrate isdesired.

One of the primary considerations when applying cladding to a drill bitor a roller cone is to avoid damaging the inserts. As noted above, priorart laser cladding techniques first apply the cladding material usingsome other technique and later fuse the cladding material onto theroller cone using laser beams. With this approach, a significant amountof energy is imparted to the bit. This often leads to cracks in thecladding. If cracks develop, the inserts may also crack, leading topremature failure of the bits. In order to avoid inadvertently crackingthe inserts, prior art techniques generally do not apply cladding to theareas immediately adjacent to the insert. However, this approach isproblematic because relatively large areas of the cone surface are leftunprotected.

Embodiments of the present invention, however, allow cladding to bedeposited over the entire surface of the cone in a one step process. Thecladding does not bond to the coated regions of the cone (which, in oneembodiment, comprises the inserts), but rather only substantially bondsto the uncoated regions.

FIG. 5 a illustrates an embodiment of the invention in accordance withone aspect of the invention. In FIG. 5 a, cone (200) includes multiplerows of inserts (206), and has a heel portion (208) located between gagerow inserts (212) and an O-ring groove (23). A plurality of protrudingheel row inserts (214) are spaced around the heel portion (208). Asshown in FIG. 5 a, a laser-assisted cladding apparatus (220) is showndepositing wear resistant layer (210) on a surface of cone (200). Inparticular, the laser-assisted cladding apparatus (220) is showndepositing the wear resistant layer (210) between two rows of teeth(206).

The laser-assisted cladding apparatus (220) is now discussed in moredetail with reference to FIG. 5 b. In general, the laser-assistedcladding apparatus (220) comprises a cladding feed line and a laser(230). In one embodiment, the cladding feed line comprises a wearresistant powder (such as tungsten carbide) feed line (240). Also, in aparticular embodiment, a portion of the powder feed line (240) and thelaser (230) are arranged so as to be “in line.” That is, the powder feedline (240) and laser (230) are disposed parallel to one another so thatthe laser energy heats the powder (and in some cases, melts a portion ofthe powder) as it is transmitted through the powder feed line into thelaser path.

Although one embodiment uses a single laser source for pre-heating thewear resistant material and for laser cladding, one of ordinary skill inthe art would appreciate that separate laser sources may be used forpre-heating and cladding.

Some of the laser beam energy also heats the substrate (namely a surfaceof the cone and/or leg). The heated or partially melted wear resistantpowder is directed (referred to as the “entrained powder”) towards thesurface of the slightly heated substrate. As a result, the heated orpartially melted wear resistant powder is deposited on the surface ofthe cone. The present inventors have discovered that a novel coating maybe applied to selected surfaces of a cone to prevent bonding of thecladding (wear resistant powder). In a particular embodiment, thecoating is applied to at least one insert to reduce damage to the insertduring the cladding process and to prevent bonding of cladding to theinsert.

A typical wear resistant powder comprises a tungsten carbide-cobaltpowder. In one embodiment, the wear resistant powder may comprise acobalt content of about 7 to 20 weight percent, a carbon content ofabout 0.5 to about 6 weight percent, and a tungsten content from about74 to 92.5 weight percent. However, depending on the particularapplication, the relative weight percents of the various chemicalcomponents may be varied. In addition, it should be understood that anywear resistant material capable of being applied by a laser claddingprocess is within the scope of the present invention.

As shown in FIG. 6, a coating 604 in accordance with embodiments of thepresent invention, may be applied over the top and side surfaces of theinsert 602, over the entire insert 602, or over selected portions of theinsert. Those having ordinary skill in the art will recognize that anumber of coatings may be suitable, so long as they provide an improvedresistance to bonding between the cladding and the substrate.

In some embodiments, the coating is a boride, nitride, or carbide of agroup IVA, VA, or VI transition metal (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,W), or mixtures thereof. In a particular embodiment, the coating is TiN.The coating 604 has been discovered to prevent the bonding of an appliedwear resistant layer to the insert 602.

By using the coating 604, it has been discovered that claddinginadvertently applied to the insert may simply be brushed off. Thus,cladding can be applied to the entire surface of the cone, withoutattempting to avoid the inserts. Accordingly, a significant timereduction in applying a cladding layer to the cone surface may berealized. This is due to the fact that by using coated inserts, wearresistant material may be deposited without regard to whether thematerial is being deposited over an insert or over the cone. Aspreviously noted, without such a coating, laser cladding of conesurfaces often causes the inserts to prematurely fail.

It should be noted that while reference is made to a cone surface andinserts disposed in the cone, the coatings of the present invention havea broader application. In particular, it is expressly within the scopeof the present invention that coatings in accordance with the presentinvention may be used generally to prevent the deposition of cladding toselected portions of a substrate.

Some embodiments of the invention relate to systems for performing thecladding process described above. A system in accordance with theinvention typically includes a processor and a memory operativelycoupled to the laser-cladding apparatus. In some embodiments, a systemmay be implemented on a general-purpose computer having a processor, amemory, and may optionally include other hardware. For example, as shownin FIG. 7, a typical computer (750) includes a processor (752), a randomaccess memory (754), and a storage device (e.g., permanent memory orhard disk) (756). The computer (750) may also include input means, suchas a keyboard (758) and a mouse (760), and output means, such as amonitor (762). Note that the general purpose computer is only forillustration and embodiments of the invention may take other forms.

In a system in accordance with the invention, the memory stores aprogram readable by the processor. The program may comprise acomputer-aided design (CAD) rendering of a drill bit on which a claddinglayer is to be deposited. The CAD rendering may include geometricinformation such as the location of the teeth, journal angle, and othersuch information as required. This information may then be transmittedto the laser-assisted cladding apparatus (shown as 220 in FIG. 5 a), sothat the wear resistant layer may be deposited in the areas surroundingthe inserts (206, 212, and/or 214) shown in FIG. 5 a, without contactingthe inserts. In this fashion, the process can be automated, wherein auser can select a stored drill bit configuration, and allow thelaser-assisted cladding apparatus (220) to deposit the cladding layerwithout further operator intervention.

FIGS. 8 a and 8 b illustrate an apparatus for applying cladding asdescribed above. In FIG. 8 a, a cone (800) is shown mounted on a fixture(802). A portion of the fixture (802) may be rotated or translated toexpose various surfaces of the cone to a laser (806). The laser (806)may similarly be rotated or translated to apply wear resistant material,which arrives to the laser head through powder inlet (810).Additionally, a moveable air flow outlet (804) may be provided to coolthe cone (800) during the cladding process.

Further, FIG. 8 a shows coated inserts (812), which have been previouslyinserted into the cone, prior to cladding. FIG. 8 b shows the apparatusof FIG. 8 a during the actual cladding process. As can be seen in FIG. 8b, the air flow outlet (804) may be moved to provide a cooling stream ofair over the cone (800) surface. This apparatus allows a relativelylarge amount of wear resistant material to be deposited in a shortamount of time.

As noted above, this apparatus and the techniques associated with theapparatus provide two different types of selectivity. These are referredto herein as positional selectivity and bonding selectivity. Bypositional selectivity, the present inventors mean that cladding may bedeposited (in a one step process) in a selected region on a cone, forexample, without contacting inserts (or plugs) on that cone.

By bonding selectivity, the present inventors mean that the inserts (orselected portions of a substrate) may be treated with a coating thatcreates a difference in the bonding strength between the inserts and thecone with respect to the cladding.

Advantageously, therefore, one or more embodiments of the presentinvention are capable of producing highly erosion-resistant hardfacingcoatings on rock bit cone surfaces to prevent cone shell erosion duringoperation. In addition, one or more embodiments of the present inventionprovide a cost effective way to reduce insert cracking often associatedwith the cladding process.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A method for applying a wear-resistant material to a rock bit,comprising: depositing a coating on a selected area of the rock bit; andapplying a heated wear-resistant material to the rock bit, wherein thecoating is selected to have material properties to prevent significantbonding between the heated wear-resistant material and the coated areaof the rock bit.
 2. The method of claim 1, wherein the selected areas ofthe rock bit comprises inserts.
 3. The method of claim 1, wherein thecoating comprises at least one selected from the group consisting of acarbide, a boride, and a nitride of a metal selected from group IVA, VA,VIA transition metal.
 4. The method of claim 1, further comprisingremoving the heated wear-resistant material from the selected area ofthe rock bit.
 5. The method of claim 1, wherein applying comprises usinga laser assisted cladding apparatus.
 6. An insert having a coating on aportion thereof for use in a rock bit, comprising: a substrate; and acoating deposited on at least one portion of said substrate in an amountsufficient to reduce bonding of a wear-resistant material to saidsubstrate.
 7. The insert of claim 7, wherein the coating comprises atleast one selected from the group consisting of a carbide, a boride, anda nitride of a metal selected from group IVA, VA, VIA transition metal.8. A method of fabricating a drill bit, comprising: forming a body ofthe drill bit; forming a plurality of holes in portions of the body toreceive coated inserts; inserting at least one coated insert into atleast one of said plurality of holes; cladding at least one selectedarea of said body with a wear-resistant material.
 9. The method of claim8, wherein the laser-assisted cladding apparatus comprises a feed lineand a laser.
 10. The method of claim 9, wherein the feed line comprisesthe wear-resistant material.
 11. The method of claim 10, furthercomprising disposing the feed line in parallel with the laser.
 12. Themethod of claim 8, further comprising cooling the drill bit.
 13. Themethod of claim 8, further comprising removing the wear-resistantmaterial from the plurality of coated inserts.
 14. The method of claim8, wherein the cladding comprises using a laser-assisted claddingapparatus.
 15. The method of claim 14, wherein the wear resistantmaterial is deposited in a single step.
 16. A system for performing acladding process, comprising: a processor; a memory operatively coupledto a laser-assisted cladding apparatus, wherein the apparatus comprisesa feed line, wherein the feed line comprises a wear-resistant material,and a laser.
 17. The system of claim 16, wherein the memory stores aprogram readable by the processor.
 18. The system of claim 17, whereinthe program contains a geometric information of a rock drill bit.
 19. Arock bit made using the method of claim
 1. 20. A rock bit comprising aninsert in accordance with claim
 6. 21. A method for selectively applyingcladding to a rock bit, comprising: depositing, in a one step process,wear resistant material on a selected region of a cone, withoutcontacting inserts on that cone.
 22. The method of claim 21, wherein theone step process comprises using a laser assisted cladding apparatus.